1. Field of the Invention
The present invention relates to a smoke detector that optically detects a contaminant such as smoke caused by fire and floating in the air, and detects the fire.
2. Description of the Related Art
A smoke detector is used for preventing fire or as a detecting system at a time of generation of the smoke or in a semiconductor manufacturing plant or a food factory requiring a certain level of environmental conservation.
The conventional smoke detector includes a smoke detection part connected to a sampling pipe, a fan that sucks sampling air into the sampling pipe, and a wind velocity sensor that measures a wind velocity of the sampling air within the sampling pipe (for example, refer to JP 3714926 B).
In the smoke detector, the sampling air flowing within the sampling pipe is partially introduced into the smoke detection part, and smoke detection is executed by a smoke sensor of the smoke detection part. After that, the sampling air is returned into the sampling air pipe. At this time, the fan is controlled on the basis of the air velocity measured by the air velocity sensor, and so controlled as to supply the sampling air as designed to the smoke detection part.
Further, the conventional smoke detector includes a smoke detection part having an inflow port and an outflow port, a sampling pipe disposed in a monitor space, an airflow pipe in which the sampling air flows, an intake side flow path branch part disposed in the airflow pipe and coupled to the inflow port of the smoke detection part, and a filter disposed between the inflow port and the intake side flow path branch part (for example, refer to JP 2000-509535 A).
In the smoke detector, a part of the sampling air flowing within the airflow pipe is introduced from an inlet of the intake side flow path branch part, and supplied to the smoke detection part after dust or the like are removed by the filter. Then, after smoke detection is executed by the smoke sensor of the smoke detection part, the sampling air is returned into the airflow pipe from the outflow port through an exhaust side flow path merging part.
As illustrated in FIG. 4, a fan 2 is incorporated into a sampling pipe 1, and an opening part 3 that sucks sampling air SA is defined at one end thereof.
When the fan (blower fan) 2 is used with a high air volume, an opening part 3a (sampling air intake) is opened large as indicated by a phantom chain line, and no disturbance of airflow which induces a reverse flow in a primary side pipe of the fan occurs in the vicinity of a suction port 4 of the fan 2.
However, when the opening part 3a is made smaller to reduce the suction air volume, the disturbance of airflow occurs within the primary side pipe of the fan due to rotation of rotor blades within the fan 2, and the reverse flow starts.
When the opening part 3a is further made as small as the opening part 3 indicated by a phantom solid line to further reduce the suction air volume, a reverse flow L circulates within the sampling pipe 1 due to the disturbance of air flow from the fan 2, and passes through an air velocity sensor 5. This makes the flow unstable in the vicinity of the air velocity sensor 5, and hence the air velocity cannot be precisely measured.
Therefore, in order to solve the above-mentioned problem, it is conceivable to sufficiently separate the air velocity sensor 5 apart from the fan 2 so as to avoid an influence of the reverse flow L, which is however not preferable since the smoke detector is upsized.